Stalker: Shadow of Chernobyl has a LOT of T2k-ish elements in it. I mean, bunches and bunches, but also of course Roadside Picnic (if you've never read this book, go find it and read it NOW) and some SFish weapons thrown in (man-portable railguns for example).
Basically if you tossed out the "anomalies" (energy fields that can kill you) and the mutants (malformed humanoids and animals that can mess you up good), then threw in a slew of NATO weapons and changed the objectives around a bit, added some western NPCs, you'd basically have it entirely.
There's even areas of dangerous fallout!
FWIW, I sat down with the "Hammer" editor for Valve Software's excellent "Source" engine to see what could be done with it. There are a ton of free weapon model resources, as well as vehicles and so on, plus AI scripting is a snap in Hammer. However, I was disappointed to find that the largest a map can be is 2048 feet on a side - less than a kilometer
. Now, a 2048x2048x2048
building full of halls and rooms, or a cleverly "culled" city block with many buildings in it of those dimensions would be titanic-seeming. However, outdoors? In a vehicle? Yeah, not so much. Pity. Apparently, that's hard-coded into the engine too.